Sean Dignam

Sean Dignam (1971-) was a Massachusetts State Police staff sergeant who served as the Undercover Unit's liaison with the Special Investigations Unit.

Biography
Sean Dignam was born in Boston, Massachusetts in 1971, and he became a Massachusetts State Police officer. Dignam's undercover work was extensive, and he later became the liaison of the MSP's undercover unit with the Special Investigations Unit. In 2006, as Captain Oliver C. Queenan's right-hand man, he recruited Billy Costigan as an undercover officer, assigning him to infiltrate the Costello Mob. Dignam also had to work with SIU officer Colin Sullivan, who was secretly a mole for the Irish Mob, and, after Queenan was killed by the Mob, Dignam resigned rather than work with Sullivan. He suspected Sullivan of being the mole after discovering that Sullivan had Queenan followed, and he decided to take revenge on Sullivan after Costigan was killed and trooper James Barrigan was framed as the mole. When Sullivan returned to his apartment with groceries, he was ambushed by Dignam, who shot and killed him as he entered.